| With the development of the air-space-ground integrated information network and the next generation mobile communications,frequency band for communications is evolving from microwave frequency band and low band of millimeter wave including Ka-band,Q-band and V-band to higher band above 100GHz(also known as terahertz or Asia-Pacific hertz).High-frequency millimeter wave has a short wavelength and narrow beam,which has a larger communication bandwidth and better security performance.It is promising for the application potential to achieve extremely high communication rates.On the other hand,in the high-dynamic communication scenario of ultra-high-speed movement,the severe Doppler frequency shift effect greatly limits the millimeter-wave communication technology based on Orthogonal Frequency Division Multiplexing(OFDM).In order to cope with this problem,Orthogonal Time Frequency Space(OTFS)that adopts the delay Doppler domain characterization method of wireless channel,is proposed to improve the performance of communication system against multipath and Doppler frequency shift by taking advantage of the sparsity and long-term stability of the delay Doppler domain channel.At present,the research on OTFS technology mainly focuses on microwave and millimeter wave low-frequency bands,and this thesis focuses on the research of key technologies of high-dynamic high-frequency millimeter-wave OTFS communications.Firstly,the background of 6G-oriented air-space-ground integrated information network technology is introduced,and the research progress of OTFS technology at different frequencies is summarized.The basic principle and theoretical model of OTFS system are expounded.Also,the relationship between the signal delay Doppler domain and the time-frequency domain based on finite symplectic Fourier transform is derived,compared with OFDM technology.The channel response matrix of the delay Doppler domain for signal estimation and channel detection is given.Accordingly,the pros and cons of three detection algorithms,zero-forcing,minimum mean square error and message passing,are analyzed and compared.Then,according to the characteristics and requirements of the high-dynamic highband millimeter-wave OTFS communication system,the OTFS signal waveform and parameter design is carried out,including the total bandwidth of the signal,carrier frequency,moving speed,number of subcarriers,number of symbols,subcarrier interval,etc.The influence of different parameters on system performance is analyzed through theoretical and simulation experiments,thus the appropriate system parameters are optimized and determined.In addition,addressing at the problem of high the Peak-toAverage Power Ratio(PAPR)of the system due to the OTFS signal with a large number of symbols,the PAPR optimization method of OTFS system based on DFT-S technology is studied.Finally,structure design of pilot symbols and method for channel estimation of highdynamic high-band millimeter-wave wideband OTFS communications are studied.The decentralized multi-pulse pilot structure is proposed to overcome the shortcomings of single-pulse pilot and centralized multi-pulse pilot.In particular,the proposed structure separates the pilot and protection symbols into one frame,and both the delay and doppler of the proposed pilot within the frame are on the same axis,while the rest are data symbols.There is no phase offset after the pilot passes through the channel,and no data overlap between different symbols.Finally,the threshold method is adopted for channel estimation for subsequent channel error analysis and system performance analysis. |
